Module to interact with interpreter's opcodes.

The interpreter's instruction set includes 36 instructions, that allow programs to perform operations of arithmetic, control flow, data manipulation, graphics, and logical.

All instructions are 2 bytes long and are stored in a big-endian format. In memory, the interpreter assumes that all instructions should start at an even address, and needs to be taken into account when adding sprite data, see Chip8.Interpreter.Display.Sprite for more information.

instruction-definition

Instruction Definition

Instructions are grouped in modules that represent their operation and share the same mnemonic, making different opcodes as simple variants. Inside each module, there is a table describing all variants supported by the module, each variant specifies its opcode and the effects applied into the interpreter once it is invoked.

Since each variant supports a different type of value as operands (i.e. arguments), the notation below is used to compactly describe the use of each part inside the opcode:

• nnn or address - A 12-bit integer value, representing an memory address
• n or nibble - A 4-bit integer value, representing a literal number
• kk or byte - An 8-bit integer value, representing a literal number
• x or Vx - A 4-bit integer value, representing one of the 16 variable registers
• y or Vy - A 4-bit integer value, representing one of the 16 variable registers

decode

Decode

# When decoding an instruction, the given 2 bytes list is transformed into a Chip8.Interpreter.Instruction.t/0, containing the module that supports the given opcode as one of its variants and the arguments, that was also parsed into its equivalent struct i.e. an nnn address is transformed into a Chip8.Interpreter.Instruction.Argument.Address.t/0.

In case an unknown segment of bytes is given, an error is returned.